This invention relates to a pesticidal composition having a pesticide suspended or emulsified in a water-based medium.
Pesticides such as insecticides, fungicides and herbicides are generally prepared into an appropriate formulation such as an emulsifiable concentrate, wettable powder, dust or granules, depending upon their individual characteristics and purpose of use, before they are put to a practical use. Recently, water-based suspension concentrates (hereinafter abbreviated into SC) having a pesticide suspended in a water-based medium and water-based concentrated emulsions (hereinafter abbreviated into EW) having a pesticide in the form of an emulsion are coming to be favorably considered from the point of view of human safety and environmental protection from these pesticidal formulations. These SCs and EWs, however, are required to be stable such that there is no sedimentation, flocculation or gelation of their suspended or emulsified particles.
Examples of dispersant conventionally used for the preparation of SCs and EWs include non-ionic surfactants such as polyoxyethylated alkylphenol, polyoxyethylated polyarylphenol, sorbitan fatty acid esters and polyoxyethylated sorbitan fatty acid esters, and anionic surfactants such as many kinds of sulfonates, sulfates and phosphates. Examples of known stabilizer for dispersion of an emulsion (protective colloid) to be used with such a dispersant include synthetic organic high molecular compounds such as carboxymethyl cellulose, polyethylene oxides and polyvinyl alcohols and natural sugar derivatives such as xanthan gum, guar gum and sodium alginate. Japanese Patent Publications Tokko 58-24401, Tokkai 61-126001 and Tokkai 63-8301 and European Patent EP-261492, for example, disclose examples of SC as water-based pesticidal formulations using these known dispersants and stabilizers. U.S. Pat. No. 4,303,640, Japanese Patent Publications Tokko 63-32046, Tokkai 58-131902 and Tokkai 63-198605 and British Patent 2,048,675, for example, disclose examples of EW as water-based pesticidal formulations using these known dispersants and stabilizers.
With these prior art SC and EW using known dispersants and stabilizers, however, there remain the problems of sedimentation, flocculation and gelation of the suspended or emulsified particles, thereby adversely affecting not only the stability of the water-based pesticidal formulations but also their handling and biological activities. In particular, the stability of a water-based pesticidal formulation decreases as its pesticide concentration increases. The viscosity of the system increases significantly in such a case and this introduces additional limitations in the selection of apparatus for its preparation as well as its load.